The present invention relates to the field of non-woven sheets, made of fibers or filaments, and intended, in particular, but not exclusively, for use in making sanitary articles, for example for disposable diapers for babies, for incontinent adults or for female sanitary protection. It relates, more especially, to a method for perforating a non-woven sheet and to an apparatus suitable for implementing this method.
There exist various methods for perforating non-woven sheets.
Document EP-A-0214608 describes a method for perforating a non-woven fabric which comprises, specifically, thermoplastic fibers or filaments. This method consists in perforating the non-woven sheet by means of a plurality of needles which cooperate with a plurality of recesses. Through the action of the needles, the fibers of the non-woven sheet are pushed back locally and, in order to preserve the void thus formed, the studs and the contour of the recesses are heated so as to cause the thermoplastic fibers to melt. After the melted fibers have hardened, a perforation is obtained that has the shape of the needle and the contours of which are delimited and consolidated by fibers that have melted and are thus welded together.
This method has the drawback, on one hand, of necessitating the use of a non-woven fabric containing thermoplastic fibers and, on the other hand, of imparting a certain amount of rigidity to the non-woven fabric owing to the presence of the hardened areas on the periphery of the perforations.
Document EP-A-0974433 describes another type of method for perforating a non-woven sheet. According to this method, the sheet is pushed by a perforating member inside a through orifice provided in a thin part in such a way that the non-woven sheet projects from said hole. Cutting means positioned inside the thin part then cut the fibers projecting from said part so as to form perforations. The perforating member is a cylindrical stud the end of which is hemispherical, and which is designed to be driven simultaneously in translation along its longitudinal axis and in rotation about its own axis. The function of this perforating member is not to cut the fibers or the filaments of the sheet, this function being performed by the cutting members. This method necessitates a relatively complex device comprising, in particular, a hollow cylinder, the interior of which is equipped with cutting members and necessitates the use of a thin part in which the orifices are provided. In addition, this method does not guarantee that perforations having a sharp contour that is reproducible in time will be obtained.